mod_expires – This module controls the setting of the Expires HTTP header in server responses. The expiration date can set to be relative to either the time the source file was last modified, or to the time of the client access.

The Expires HTTP header is an instruction to the client about the document’s validity and persistence. If cached, the document may be fetched from the cache rather than from the source until this time has passed. After that, the cache copy is considered “expired” and invalid, and a new copy must be obtained from the source.

mod_expires is included in most default installs.

Check wheter LoadModule expires_module modules/mod_expires.so is enabled or not in httpd.conf, if its not then uncomment it removing the # prefix.

And then add following code into your httpd.conf configuration file -

Restart apache server.

Resource links -

http://blog.cherouvim.com/mod_expires-and-cache-killers/
http://httpd.apache.org/docs/1.3/mod/mod_expires.html
http://www.david-guerrero.com/papers/squid/squid.htm
http://linuxreviews.org/webdesign/602_Apache_mod_expire/
http://jeremy.zawodny.com/blog/archives/009272.html

If Apache 2.0 is running on several Linux boxes behind a load balancer, here are a couple of things you can do to speed things up.

1. Disable RedirectMatch directives temporarily

2. Increase MaxClients and ServerLimit

This is a well-known Apache performance optimization tip. Its effect is to increase the number of httpd processes available to service the HTTP requests.

The 2 entries in httpd.conf, in IfModule prefork.c section are:

MaxClients 1000
ServerLimit 1000

Now there is a procedure for tuning the number of httpd processes on a given box:

1. Start small, with the default MaxClients (150).
2. If Apache seems sluggish, start increasing both MaxClients and ServerLimit; restart httpd every time you do this.
3. Monitor the number of httpd processes; you can use something like:

ps -def | grep httpd | grep -v grep | wc -l

If the number of httpd processes becomes equal to the MaxClients limit you specified in httpd.conf, check your CPU and memory (via top or vmstat). If the system is not yet overloaded, go to step 2. If the system is overloaded, it’s time to put another server in the server farm behind the load balancer.

WARNING: MaxClients of 1000 exceeds ServerLimit value of 256 servers, lowering MaxClients to 256. To increase, please see the ServerLimit directive.

To avoid above warning, You need to put the Serverlimit option before the maxclient in the apache config file.

Example config:

IfModule prefork.c

StartServers 20
MinSpareServers 5
MaxSpareServers 20

ServerLimit 1024 <====—— moved this line here rather than after the
Maxclients (otherwise Apache will gives error, “WARNING: MaxClients of 1000
exceeds ServerLimit value of 256 servers, lowering MaxClients to 256. To
increase, please see the ServerLimit directive”)

MaxClients 512 <====——– changed from 256 to 512

MaxRequestsPerChild 10000

IfModule

Apache 2.x is designed to balance flexibility, performance and portability. Apache is a good all-purpose webserver. Since Apache is designed to fit most scenarios it hasn’t been optimized to set any kind of speed records, but Apache 2.x is capable of high performance.

There have been many improvements made in Apache 2.x and many are enabled by default. But, there are some changes you can make at compile-time and run-time that can positively affect performance.

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